The invention relates to a method of manufacturing a structural element having a metal wall of generally tubular shape with at least two segments that are not in axial alignment, and it also relates to a tubular metal-walled structural element suitable for being made in a very wide variety of shapes and for a very wide variety of applications.
In numerous industrial sectors, it is necessary to have structural elements of generally tubular shape, that comprise successive segments that are not in axial alignment, and that are of cross-section that is more or less complex in shape, and in particular that is polygonal.
Such structural elements may be curved or may present successive segments that are rectilinear in angular dispositions, for example extending at right angles to one another, when providing structural elements in the form of square or rectangular frames.
In certain applications, it is necessary to have frames presenting high stiffness and mass that is as low as possible, with these two conditions generally being difficult to reconcile when making frames by assembling together tubular section members of polygonal section. In order to assemble and weld together the sides of the frame at its corners, it is necessary to use tubes having walls of sufficient thickness. As a general rule, it is difficult to make frames by assembling tubes together, e.g. tubes of square section, if they have wall thickness that is less than 1 millimeter (mm).
In certain applications, for example in making metal doors, it can be desirable not only to obtain good stiffness and mass that is as light as possible, but also to obtain qualities making the door appealing to the eye, for example when the door is used in a building where a particular decorative style is implemented. Under such circumstances, it can be necessary to provide framework structures with different sides presenting sections of various shapes. It is therefore necessary to have tubes with sections of different shapes and possibly shapes that are most unusual. This makes the construction of such doors very expensive.
In certain industries, for example the automobile industry, the aviation industry, or the ship-building industry, structural elements or “chords” are used that are light in weight, that have tubular metal walls, that are complex in shape, and that may be curved or even looped back onto themselves in order to constitute an annular piece. Such structural elements whose tubular structure serves to obtain savings in weight must be built in a manner that is extremely stiff and strong.
In order to make such complex structures, it is generally necessary to assemble together a large number of pieces that have previously been shaped by a forming and/or cutting-out method. Assembling pieces together to make a structure of complex shape, and to do so with good precision both in shape and in dimensions, is an operation that is expensive, and the various welds used to build the assembly must be inspected thoroughly.
In addition, when the metal material used is difficult to weld, such as aluminum and its alloys, it is even more difficult and expensive to make complex structures, and it may be necessary to use assembly methods that are difficult to implement in order to avoid the presence of welding.
When making structural elements from flat materials such as metal sheets, blanks are generally cut out and assembled together by being welded along their edges, which generally requires the use of jigs and supports for holding the blanks in their assembly position. Such structures are therefore complex to make and require the use of tooling that is expensive. In addition, in certain circumstances, it is not even possible to use a jig placed in a hollow portion of the tubular structure because the shape of the structure would prevent the jig from being removed after the structure has been assembled and welded together.